Patent GB-498741-A (GB)
Title: Improvements in and relating to telephone installations
IPC: H04Q3/00
Filed: 1937-06-07
Abstract: 498,741. Automatic exchange systems. LEHNER, C., GADESMANN, M., LEICHTHAMMER, K., and LEICHTHAMMER. H., (trading as TELEFONBAU UND NORMALZEIT LEHNER & CO.). June 7, 1937, No. 15775. Convention date, June 5, 1936. [Class 40 (iv)] In an inter-exchange system, the tones for indicating the condition of the wanted line are generated at the first selector and are controlled from the final selector by backward signals which within the exchanges consist of strong or weak currents over one speech wire and over the junction consist of A.C. impulses of different lengths. Local connection. Upon the initiation of a call, two-step line and cut-off relay T operates contacts t1, t2, and causes the finder AS to rotate into engage- - ment with the calling line. Relay T energizes fully and connects up R, while line relays A, B energize over the loop, dialling tone being sent inductively through the windings of these relays from lead s1 The group and final selectors GW, LW are set by impulses in the usual way and the wanted line is tested by 4P on the relapse of dialling relay V. Relay 4R, which is connected up by V at this time, disconnects 4V, which after an interval opens the test circuit. If the wanted line is busy, 4P is inoperative, and the relapse of 4V connects battery through a high resistance W1 to the b wire. In the group selector GW, relay M energizes in series with marginal relay Fr, which is inoperative, and applies busy tone from lead s2. If it is desired to release the switch train, relay M also short-circuits release relay C to bring this about, and relay T reverts to its condition of partial energization over the loop, which now includes R, so that busy tone is sent inductively over the windings of T. If the wanted line is idle, the operation of 4P connects battery through a low resistance W2 to the b wire, this being interrupted when 4U falls back and replaced when back-bridge relay 4Y pulls up. 'Relay Fr in the group selector responds as well as M, applies a continuous tone from lead s3 and connects two-step relay Z to the b wire. The latter energizes partially in series with Fr, M when the backward signal is interrupted and substitutes a periodic tone from lead s4 for the continuous tone, and energizes fully when the signal is replaced and prepares a metering circuit. Relay M may also be arranged to operate to send a busy signal when the group selector moves to an overflow position. Inter-exchange connection. Upon the seizure of the outgoing repeater U1, relay 2C energizes and connects up impulse relay 2A during the slow operating period of 2U, so that an A.C. impulse is sent over the junction. This is received in the incoming repeater U2 by impulse relay 3A and connects up 3C which seizes the final selector LW. Numerical impulses are repeated by A, 2A, 3A to line relay 4A, and the wanted line is tested. If the line is busy, battery through high resistance W1 energizes 3M in series with K, which is inoperative, and a long A.C. impulse is returned over the junction by 3S during the slow release period of 3N, which is short-circuited by 3M. Relay 2W responds, connects up Y and shortcircuits 2N, so that at the end of the impulse X pulls up and connects battery through a high resistance W3 to wire b to operate M as described above. If the wanted line is idle, battery through low resistance W2 energizes K, which nullifies the effect of 3M, and a short A.C. impulse is sent during the slow operating period of L. Relay 2W responds and connects up Y, but 2N holds until the end of the impulse so that the operation of X connects battery through a low resistance W4 to the b wire to operate Fr as described above. On the relapse of K, a second short impulse is sent during the slow release period of L, and this disconnects Y, so that X, which is held over a second winding during the impulse, falls back at the end of it and opens the connection to the b wire, so that Z energizes partially. The reconnection of battery through. W2 when 4Y pulls up acts in a similar manner to send a short impulse which operates X and causes Z to energize fully.